27 hours 3 minutes and 44 seconds.
Possibly:https://www.john-cage.halberstadt.de/new/index.php?seite=dasprojekt&l=e
This is the only 'classical music' type thing that I've ever heard on a rock radio station in a while. I live in Ottawa, and a little bit on this performance came up and I was pretty impressed, because I wouldn't expect an alternative rock station to say much about this.
Paul Jacobs, the famous organist (not pianist), has on many occasions played Bach's complete organ works in concert without stopping. That takes over 18 hours to do. I find that much more impressive than what this hack did, which wasn't even classical. It was basically a one man jam session, which I'm sure anyone else could do with all that material flying at the (from the audience).
I personally don't find this very impressive. It seems people do this sort of stuff all the time to get attention.
I'd just play the moonlight sonata VERY slowly :p